1. Technical Field
The present invention relates to a diisononyl terephthalate (DINT) suitably used as a plasticizer and if used in plastic products having a property of low plasticizer migration, and more particularly relates to a process for producing the DINT plasticizer.
2. Description of Related Art
Plasticizers have been extensively used in the plastic industry such as functionally used as coating materials, filling and reinforcing material, and processing aids. Thermoplastics effectively promote physical effects via plasticizers added thereto, since plasticizers when dissolved in thermoplastics form a Homogeneous phase, and provide swelling effects. As compared to thermoplastics without plasticizers added, those thermoplastics having plasticizers added enjoy advantages including said thermoplastics are processed under much lower processing temperature and said thermoplastics are allowed to become more excellent in better flowability when heated for molding as well as more favorite in both elasticity improved and rigidity reduced.
Plasticizers are extensively used as long as their use is odorless, colorless, UV resistant, cold-resistant, heat-resistant, hydrolysis-resistant, flame-retardant, less volatile and safe to human health as the final products require. In addition, manufacturing of plasticizers is required to be simple and environmental friendly, and preferably does not generate undesired by-products and polluted wastewater.
An esterified product synthesized from acids and alcohols may be used to produce a plasticizer. Therein, the acids include dicarboxylic acid and polycarboxylic acid, and the alcohols include straight- or branched-chain alcohols having 6-13 carbons as well as may be a single compound or a mixture.
In a basic process for producing an esterified product, acids or acid anhydrides and alcohols or mixed alcohols react in the presence of an acid (e.g. sulfuric acid) as a catalyst for esterification. During synthesis, the reactive alcohols have to be used in an excess amount, and the acid acting as the catalyst is such controlled during synthesis that it does not cause the esterified product to have undesirable smell or poor hue. Therefore, the process requires mild reaction conditions and multiple purifying steps.
According to current technical level, catalysts often used for synthesizing the ester plasticizer are metal-containing esterification catalysts, including tin-containing, titanium-containing or zirconium-containing esterification catalysts, and tin-containing, titanium-containing or zirconium-containing salts, oxides and dissoluable organic compounds. Metallic catalysts of this type are esterification catalysts used at a temperature higher than 180° C., such as tin powder, tin oxide, organic titanate, and organic zirconates (including tetrabutyl zirconate, alkyl titanate, titanium chelate, etc.).
There are two ways to prepare the ester plasticizer, namely esterification and hydrogenization. U.S. Pat. No. 6,310,235B1 discloses a method for preparing the ester plasticizers through esterification, wherein an acid (such as dicarboxylic acid or polycarboxylic acid or acid anhydride) and an alcohol perform esterification in the presence of a titanium-containing or zirconium-containing or tin-containing metal catalyst. The esterification is carried out in two stages. In the first stage, the temperatures to be employed is relatively low (120-160° C.) for forming a monoester. Then the temperature is raised to 250° C. and a catalyst is added for bis-esterification. Afterward, neutralization is performed using an alkali-containing or alkali-earth-metal-containing aqueous hydroxide solution, follows by removing excess reactive alcohol, drying and filtering, so as to obtain an esterified product used to produce a plasticizer. Nevertheless, such a process for esterification is disadvantageous for requiring relatively long reaction time.
The plasticizers commonly used today include phthalate-type plasticizers such as diisooctyl phthalate (DIOP) plasticizers, diisononyl phthalate (DINP) plasticizers and di(2-ethylhexyl) terephthalate (DOTP) plasticizer. However, according to the relevant literatures, phthalate-containing plasticizers may generate environmental hormone that can cause great danger to organisms and their environment.
While a di(2-ethylhexyl) terephthalate (DOTP) plasticizer is acceptable in terms of environmental protection and has a glass transition temperature (Tg) of −82° C., it tends to migrate to the surface of the final products (hereinafter referred to as plasticizer migration), particularly when it is used in manufacturing of soft PVC products that requires large use of plasticizers. When final PVC products require an amount of plasticizer to reach 70 PHR, the plasticizer migration rate is greater than 2.5%, leading to degraded appearance of the final PVC products.